The present disclosure relates to power consumption measurement and, more particularly, to power consumption measurement for residential application.
Multi-phase power consumption measurement has been done in industry and by utilities for many years. Typically 2-phase power consumption has been measured at the electricity meters on the sides of homes, and 3-phase power consumption in industry use measured by electricity meters or other devices installed at the industrial location.
The equation used to describe the measurement of power consumption is:
  Energy  ≡      ∫                  ∑        i                                      ⁢                                    V            i                    ·                      I            i                          ⁢                  ⅆ          t                    where V and I are the voltage and current in each phase expressed as a vector.
There are many electrical circuits and electromechanical devices to make these measurements. Such devices generally take a voltage and a current input. Most recently, such devices typically take a voltage and current measurement for each phase and capture them many times a second and then multiply the instantaneous voltage by the instantaneous current. These values are then stored in a register and normalized to watt-seconds by dividing by the number of samples per second. Examples of existing devices that measure power consumption include the Teridian 78M6612-IGTR/F manufactured by Teridian Semiconductor Corp., or ST Microelectonics STPM Family.
In a residential application, however, such prior art approaches are problematic because they generally require two voltage references and two current measurements. Measuring current in a residential application is relatively straightforward and without significant risk. Conventionally, two clamp-on current transformers (CTs) are placed inside a residential power distribution panel and the low voltage leads brought out of the panel and connected to the power measurement device. This generally does not require making any electrical contacts in the box, and makes the installation of the CTs within the range of most handy-men.
To get two voltage references, however, two connections need to be made in the panel and high voltage leads brought out of the panel, requiring more care to comply with code and safety regulations. Thus, rather than measure voltage, many prior art devices simply assume a voltage (such as 120 volts for a residential application). This results in less accurate measurements since in many instances the actual voltage will not equal the assumed value.